1. Field of the Invention
The present invention relates to a carrier tape conveying device which is used in assembly processes of electronic components such as semiconductor elements, etc., and more particularly to a conveying device that conveys an electronic component carrier tape constructed from a soft, heat-resistant flexible material such as a synthetic resin (referred to as a xe2x80x9cresin filmxe2x80x9d) in the direction of length of the carrier tape.
2. Prior Art
The carrier tape system widely used in semiconductor element assembly processes uses a carrier tape in which a conductive layer is formed on appropriate portions of the top surface of a band-form film made of a synthetic resin. In this system, various types of assembly processes are performed by separate working devices for the respective working processes. For instance, an arrangement and bonding of numerous silicon chips to the top surface or undersurface of the carrier tape (die bonding), a connection of the surface electrodes of the silicon chips to a conductive layer by conductive wires (a wire bonding method), and a sealing of these parts with a synthetic resin (packaging) are performed.
FIG. 6 shows one of the conventionally used carrier tape conveying devices used in such carrier tape systems.
In this carrier tape conveying device, pressing rollers 75 are disposed on the top surface sides of the side edge portions of the carrier tape 2, and drive rollers 77 are disposed on the undersurface sides of these side edge portions. The rotating shafts of the pressing rollers 75 are supported so that they rotate on pressing frames 29 that are constantly driven downward. The rotating shafts of the drive rollers 77 are connected to motors 41.
In this construction, both side edge portions of the carrier tape 2 are pressure-held between the pressing rollers 75 and drive rollers 77 as a result of the driving force of the pressing frames 29. The carrier tape 2 is conveyed in the direction of its own length (i.e. in the direction perpendicular to the surface of the drawing sheet) by the driving of the motors 41. When a silicon chip 70 bonded to the undersurface of the conveyed carrier tape 2 stops at a specified working position, a jig 24 containing a heater used for preparatory heating is raised. As a result, the silicon chip 70 on the undersurface of the carrier tape 2 is received in a retaining hole 26 formed in the jig 24, and the upper surface of the carrier tape 2 is pressed by a clamp (not shown). Then, the carrier tape 2 and silicon chip 70 in this attitude are subjected to working such as wire bonding, etc. from above.
However, the carrier tape 2 is flexible and is softened by preparatory heating by the heater. Accordingly, a sag in the direction of width as indicated by the one-dot chain line 72 in FIG. 6 is generated in the carrier tape 2 by the weight of the silicon chips 70 bonded to the carrier tape 2. In cases where conveying is continued in this state, the silicon chips 70 may collide with the waiting jig 24 if the sagging is severe, and the silicon chips 70 are subjected to impacts and vibrations. Furthermore, in the case of such collisions or in cases where the extraction of the silicon chips 70 from the jig 24 is insufficient, the carrier tape 2 may be pulled by an excessive force, so that stretching or shifting of the holding position occurs in the carrier tape 2, causing a drop in conveying precision and working precision.
Accordingly, the object of the present invention is to provide a conveying device that is able to prevent sagging of the carrier tape across the width thereof during conveying before such sagging occurs.
The object is accomplished by a unique structure for a device for conveying a carrier tape for an electronic component in which the side edge portions of a carrier tape are pressure-held from its upper and under surfaces by a pair of rollers rotating in opposite directions so as to convey the tape in the direction of length thereof; and in the present invention, a supporting member which protrudes upward with respect to the pressure-holding position of the rollers is provided on the center side of the carrier tape with respect to the direction of width of the carrier tape in the pressure-holding positions of the rollers, so that the carrier tape is held by the pair of rollers and supporting member while being elastically deformed so as to allow its own recovery from the deformed state.
In this structure, the supporting member which protrudes upward in the pressure-holding positions of the pair of rollers (that pressure-hold the carrier tape) is installed further toward the center of the carrier tape with respect to the direction of width of the carrier tape. Accordingly, when the rollers apply a pressure to the side edge portions of the carrier tape, the portion of the carrier tape that is near the center of the carrier tape with respect to its width direction is lifted upward in response to this pressure with the contact points between the carrier tape and the supporting member acting as fulcrums. Furthermore, since the rollers hold the carrier tape while causing an elastic deformation thereof, the holding force of the rollers is reinforced by the recovery force of the carrier tape, and slipping between the respective rollers and the carrier tape is prevented. Sagging of the carrier tape across the width of the carrier tape can thus be prevented in advance.
Furthermore, since the rollers and the supporting member merely cause an elastic deformation of the carrier tape and do not cause plastic deformation of the carrier tape, the carrier tape recovers to its original flat shape after passing through the pressure-holding or the rollers. Accordingly, the original shape of the carrier tape can be maintained without any folds being formed in the carrier tape, and there is no danger of a drop in the conveying precision or working precision that would be caused by plastic deformation of the carrier tape.
The above-described pair of rollers comprises a first roller and a second roller. The first roller has a large-diameter portion and a small-diameter portion. The large-diameter portion is formed on the side of the roller that is located further toward the center of the carrier tape with respect to the width of the carrier tape, and the small-diameter portion is formed on the side of the roller that is located further toward the outer edge of the carrier tape. The outer circumferential surface of the second roller faces the outer circumferential surface of the small-diameter portion of the first roller. The large-diameter portion of the first roller constitutes the supporting member.
Accordingly, the supporting member is formed as an integral part to the first roller. Thus, the structure is simpler than in cases where the roller and supporting member are formed as separate parts. Furthermore, regardless of the assembly precision of the rollers, the difference in height positions between the outer circumferential surface of the small-diameter portion of the first roller (which is the pressure-holding position of the side edge portion of the carrier tape) and the outer circumferential surface of the large-diameter portion of the first roller (which is the holding position of the center side of the carrier tape) can be accurately maintained.
Furthermore, a feeding movement of the carrier tape is imparted by the first roller using its small-diameter portion (which constitutes the pressure-holding position) and its large-diameter portion (which constitutes the supporting member). Here, however, the small-diameter portion and large-diameter portion are integral and rotate together; accordingly, the feeding movement created by the large-diameter portion is greater than the feeding movement created by the small-diameter portion. In other words, the feeding movement of the center side of the carrier tape is greater than the feeding movement of the side edge portion of the carrier tape. Accordingly, the carrier tape that passes through the gap between the first roller and second roller is applied with a tension in the direction of the side edge. Thus, sagging of the carrier tape across the width of the carrier tape can be effectively prevented.
In the present invention, the width of the outer circumferential surface of the large-diameter portion of the second roller is formed so as to be equal to or greater than the width of the outer circumferential surface of the large-diameter portion of the first roller.
Accordingly, the contact area of the outer circumferential surface of the large-diameter portion of the second roller with the carrier tape is larger than the contact area of the outer circumferential surface of the large-diameter portion of the first roller. Thus, the carrier tape conforms well to the outer circumferential surface of the second roller, and the carrier tape is strongly held and elastically deformed. Consequently, sagging of the carrier tape in the direction of width of the carrier tape can be further effectively prevented.
Furthermore, the object is further accomplished by another unique structure for a carrier tape conveying device in which each of the side edge portions of a carrier tape is held under pressure from its upper and under surfaces by a pair of rollers that is comprised of first and second rollers rotating in opposite directions so as to covey the tape in the direction of length thereof; and in the present invention,
the outer circumferential surface of the first roller faces both an outer layer formed on one surface of the carrier tape and an exposed portion of the carrier tape that is located further toward the side edge of the carrier tape than the outer layer,
the outer circumferential surface of a large-diameter portion of the second roller faces the other side of the exposed portion of the inner layer of the carrier tape, and
the first and second rollers hold the side edge of the outer layer and the surface of the exposed portion at an equal height along the outer circumferential surface of the first roller while elastically deforming the carrier tape in a recoverable manner.
In this structure, when the carrier tape is pressure-held by the first and second rollers, the side edge of the outer layer of the carrier tape and the surface of the exposed portion of the carrier tape are held at equal height positions along the outer circumferential surface of the first roller while the carrier tape is being elastically deformed against its own recovery force. Accordingly, the carrier tape can be elastically deformed while utilizing the thickness of the outer layer as a spacer. Thus, since the rollers hold the carrier tape while causing elastic deformation of the carrier tape, the holding force of the rollers is reinforced by the recovery force of the carrier tape, and slipping between the respective rollers and the carrier tape is prevented. Furthermore, since the side edge of the outer layer and the surface of the exposed portion are held at equal height positions along the outer circumferential surface of the first roller, the exposed portion of the carrier tape is sufficiently supported on the first roller. Thus, the carrier tape can be held under a strong pressure so that sagging of the carrier tape in the direction of width caused by the slipping of the carrier tape from the rollers can be effectively prevented.
Furthermore, in the present invention, in addition to the above-described structures, pairs of rollers are installed on one side of a working head, which is used to perform a specific work on the carrier tape, so that the rollers are rotated and convey the carrier tape away from the working head; and a resistance means which holds the carrier tape against the moving force of the pairs of rollers is further installed on another side of the working head.
In this structure, the carrier tape is conveyed while a state of tension is maintained in the direction of length between the rollers and the resistance means. In this case, however, waviness or warping of the carrier tape in the direction of width may be generated as a result of local stretching of the carrier tape in the direction of the length. However, the central portion of the carrier tape is constantly lifted; and sagging of the carrier tape in the direction of width can be prevented.
Furthermore, even if local stretching in the direction of length of the carrier tape occurs in areas of the carrier tape located in the vicinity of the rollers, a deformation of the central portion of the carrier tape is prevented.